package com.bulemobi.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {

	// 十六进制下数字到字符的映射数组
	private final static String[] hexDigits = { "0", "1", "2", "3", "4", "5",
			"6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };

	/**
	 * 对字符串进行MD5加密
	 * 
	 * @throws java.security.NoSuchAlgorithmException
	 */
	public static String encodeByMD5(String originString)
			throws NoSuchAlgorithmException {
		if (originString != null) {
			// 创建具有指定算法名称的信息摘要
			MessageDigest md = MessageDigest.getInstance("MD5");
			// 使用指定的字节数组对摘要进行最后更新，然后完成摘要计算
			byte[] results = md.digest(originString.getBytes());
			// 将得到的字节数组变成字符串返回
			String resultString = byteArrayToHexString(results);
			return resultString.toUpperCase();
		}
		return null;
	}

	/**
	 * 转换字节数组为十六进制字符串
	 * 
	 * @param b
	 *            字节数组
	 * @return 十六进制字符串
	 */
	private static String byteArrayToHexString(byte[] b) {
		StringBuffer resultSb = new StringBuffer();
		for (int i = 0; i < b.length; i++) {
			resultSb.append(byteToHexString(b[i]));
		}
		return resultSb.toString();
	}

	/** 将一个字节转化成十六进制形式的字符串 */
	private static String byteToHexString(byte b) {
		int n = b;
		if (n < 0)
			n = 256 + n;
		int d1 = n / 16;
		int d2 = n % 16;
		return hexDigits[d1] + hexDigits[d2];
	}

}
